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Side Lights On Astronomy

S >> Simon Newcomb >> Side Lights On Astronomy



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SIDE-LIGHTS ON ASTRONOMY

AND KINDRED FIELDS OF POPULAR SCIENCE


ESSAYS AND ADDRESSES


BY SIMON NEWCOMB




CONTENTS


PREFACE

I. THE UNSOLVED PROBLEMS OF ASTRONOMY
II. THE NEW PROBLEMS OF THE UNIVERSE
III. THE STRUCTURE OF THE UNIVERSE
IV. THE EXTENT OF THE UNIVERSE
V. MAKING AND USING A TELESCOPE
VI. WHAT THE ASTRONOMERS ARE DOING
VII. LIFE IN THE UNIVERSE
VIII. HOW THE PLANETS ARE WEIGHED
IX. THE MARINER'S COMPASS
X. THE FAIRYLAND OF GEOMETRY
XI. THE ORGANIZATION OF SCIENTIFIC RESEARCH
XII. CAN WE MAKE IT RAIN?
XIII. THE ASTRONOMICAL EPHEMERIS AND NAUTICAL ALMANAC
XIV. THE WORLD'S DEBT TO ASTRONOMY
XV. AN ASTRONOMICAL FRIENDSHIP
XVI. THE EVOLUTION OF THE SCIENTIFIC INVESTIGATOR
XVII. THE EVOLUTION OF ASTRONOMICAL KNOWLEDGE
XVIII. ASPECTS OF AMERICAN ASTRONOMY
XIX. THE UNIVERSE AS AN ORGANISM
XX. THE RELATION OF SCIENTIFIC METHOD TO SOCIAL PROGRESS
XXI. THE OUTLOOK FOR THE FLYING-MACHINE




ILLUSTRATIONS

SIMON NEWCOMB

PHOTOGRAPH OP THE CORONA OP THE SUN, TAKEN IN TRIPOLI DURING TOTAL
ECLIPSE OF AUGUST 30, 1905.

A TYPICAL STAR CLUSTER-CENTAURI

THE GLASS DISK

THE OPTICIAN'S TOOL

THE OPTICIAN'S TOOL

GRINDING A LARGE LENS

IMAGE OF CANDLE-FLAME IN OBJECT-GLASS

TESTING ADJUSTMENT OF OBJECT-GLASS

A VERY PRIMITIVE MOUNTING FOR A TELESCOPE

THE HUYGHENIAN EYE-PIECE

SECTION OF THE PRIMITIVE MOUNTING

SPECTRAL IMAGES OF STARS, THE UPPER LINE SHOWING HOW THEY APPEAR
WITH THE EYE-PIECE PUSHED IN, THE LOWER WITH THE EYE-PIECE DRAWN
OUT

THE GREAT REFRACTOR OF THE NATIONAL OBSERVATORY AT WASHINGTON

THE "BROKEN-BACKED COMET-SEEKER"

NEBULA IN ORION

DIP OF THE MAGNETIC NEEDLE IN VARIOUS LATITUDES

STAR SPECTRA

PROFESSOR LANGLEY'S AIR-SHIP






PREFACE

In preparing and issuing this collection of essays and addresses,
the author has yielded to what he could not but regard as the too
flattering judgment of the publishers. Having done this, it became
incumbent to do what he could to justify their good opinion by
revising the material and bringing it up to date. Interest rather
than unity of thought has determined the selection.

A prominent theme in the collection is that of the structure,
extent, and duration of the universe. Here some repetition of
ideas was found unavoidable, in a case where what is substantially
a single theme has been treated in the various forms which it
assumed in the light of constantly growing knowledge. If the
critical reader finds this a defect, the author can plead in
extenuation only the difficulty of avoiding it under the
circumstances. Although mainly astronomical, a number of
discussions relating to general scientific subjects have been
included.

Acknowledgment is due to the proprietors of the various
periodicals from the pages of which most of the essays have been
taken. Besides Harper's Magazine and the North American Review,
these include McClure's Magazine, from which were taken the
articles "The Unsolved Problems of Astronomy" and "How the Planets
are Weighed." "The Structure of the Universe" appeared in the
International Monthly, now the International Quarterly; "The
Outlook for the Flying-Machine" is mainly from The New York
Independent, but in part from McClure's Magazine; "The World's
Debt to Astronomy" is from The Chautauquan; and "An Astronomical
Friendship" from the Atlantic Monthly.

SIMON NEWCOMB. WASHINGTON, JUNE, 1906.




I

THE UNSOLVED PROBLEMS OF ASTRONOMY


The reader already knows what the solar system is: an immense
central body, the sun, with a number of planets revolving round it
at various distances. On one of these planets we dwell. Vast,
indeed, are the distances of the planets when measured by our
terrestrial standards. A cannon-ball fired from the earth to
celebrate the signing of the Declaration of Independence, and
continuing its course ever since with a velocity of eighteen
hundred feet per second, would not yet be half-way to the orbit of
Neptune, the outer planet. And yet the thousands of stars which
stud the heavens are at distances so much greater than that of
Neptune that our solar system is like a little colony, separated
from the rest of the universe by an ocean of void space almost
immeasurable in extent. The orbit of the earth round the sun is of
such size that a railway train running sixty miles an hour, with
never a stop, would take about three hundred and fifty years to
cross it. Represent this orbit by a lady's finger-ring. Then the
nearest fixed star will be about a mile and a half away; the next
more than two miles; a few more from three to twenty miles; the
great body at scores or hundreds of miles. Imagine the stars thus
scattered from the Atlantic to the Mississippi, and keep this
little finger-ring in mind as the orbit of the earth, and one may
have some idea of the extent of the universe.

One of the most beautiful stars in the heavens, and one that can
be seen most of the year, is a Lyrae, or Alpha of the Lyre, known
also as Vega. In a spring evening it may be seen in the northeast,
in the later summer near the zenith, in the autumn in the
northwest. On the scale we have laid down with the earth's orbit
as a finger-ring, its distance would be some eight or ten miles.
The small stars around it in the same constellation are probably
ten, twenty, or fifty times as far.

Now, the greatest fact which modern science has brought to light
is that our whole solar system, including the sun, with all its
planets, is on a journey towards the constellation Lyra. During
our whole lives, in all probability during the whole of human
history, we have been flying unceasingly towards this beautiful
constellation with a speed to which no motion on earth can
compare. The speed has recently been determined with a fair degree
of certainty, though not with entire exactness; it is about ten
miles a second, and therefore not far from three hundred millions
of miles a year. But whatever it may be, it is unceasing and
unchanging; for us mortals eternal. We are nearer the
constellation by five or six hundred miles every minute we live;
we are nearer to it now than we were ten years ago by thousands of
millions of miles, and every future generation of our race will be
nearer than its predecessor by thousands of millions of miles.

When, where, and how, if ever, did this journey begin--when,
where, and how, if ever, will it end? This is the greatest of the
unsolved problems of astronomy. An astronomer who should watch the
heavens for ten thousand years might gather some faint suggestion
of an answer, or he might not. All we can do is to seek for some
hints by study and comparison with other stars.

The stars are suns. To put it in another way, the sun is one of
the stars, and rather a small one at that. If the sun is moving in
the way I have described, may not the stars also be in motion,
each on a journey of its own through the wilderness of space? To
this question astronomy gives an affirmative answer. Most of the
stars nearest to us are found to be in motion, some faster than
the sun, some more slowly, and the same is doubtless true of all;
only the century of accurate observations at our disposal does not
show the motion of the distant ones. A given motion seems slower
the more distant the moving body; we have to watch a steamship on
the horizon some little time to see that she moves at all. Thus it
is that the unsolved problem of the motion of our sun is only one
branch of a yet more stupendous one: What mean the motions of the
stars--how did they begin, and how, if ever, will they end? So far
as we can yet see, each star is going straight ahead on its own
journey, without regard to its neighbors, if other stars can be so
called. Is each describing some vast orbit which, though looking
like a straight line during the short period of our observation,
will really be seen to curve after ten thousand or a hundred
thousand years, or will it go straight on forever? If the laws of
motion are true for all space and all time, as we are forced to
believe, then each moving star will go on in an unbending line
forever unless hindered by the attraction of other stars. If they
go on thus, they must, after countless years, scatter in all
directions, so that the inhabitants of each shall see only a
black, starless sky.

Mathematical science can throw only a few glimmers of light on the
questions thus suggested. From what little we know of the masses,
distances, and numbers of the stars we see a possibility that the
more slow-moving ones may, in long ages, be stopped in their
onward courses or brought into orbits of some sort by the
attraction of their millions of fellows. But it is hard to admit
even this possibility in the case of the swift-moving ones.
Attraction, varying as the inverse square of the distance,
diminishes so rapidly as the distance increases that, at the
distances which separate the stars, it is small indeed. We could
not, with the most delicate balance that science has yet invented,
even show the attraction of the greatest known star. So far as we
know, the two swiftest-moving stars are, first, Arcturus, and,
second, one known in astronomy as 1830 Groombridge, the latter so
called because it was first observed by the astronomer
Groombridge, and is numbered 1830 in his catalogue of stars. If
our determinations of the distances of these bodies are to be
relied on, the velocity of their motion cannot be much less than
two hundred miles a second. They would make the circuit of the
earth every two or three minutes. A body massive enough to control
this motion would throw a large part of the universe into
disorder. Thus the problem where these stars came from and where
they are going is for us insoluble, and is all the more so from
the fact that the swiftly moving stars are moving in different
directions and seem to have no connection with each other or with
any known star.

It must not be supposed that these enormous velocities seem so to
us. Not one of them, even the greatest, would be visible to the
naked eye until after years of watching. On our finger-ring scale,
1830 Groombridge would be some ten miles and Arcturus thirty or
forty miles away. Either of them would be moving only two or three
feet in a year. To the oldest Assyrian priests Lyra looked much as
it does to us to-day. Among the bright and well-known stars
Arcturus has the most rapid apparent motion, yet Job himself would
not to-day see that its position had changed, unless he had noted
it with more exactness than any astronomer of his time.

Another unsolved problem among the greatest which present
themselves to the astronomer is that of the size of the universe
of stars. We know that several thousand of these bodies are
visible to the naked eye; moderate telescopes show us millions;
our giant telescopes of the present time, when used as cameras to
photograph the heavens, show a number past count, perhaps one
hundred millions. Are all these stars only those few which happen
to be near us in a universe extending out without end, or do they
form a collection of stars outside of which is empty infinite
space? In other words, has the universe a boundary? Taken in its
widest scope this question must always remain unanswered by us
mortals because, even if we should discover a boundary within
which all the stars and clusters we ever can know are contained,
and outside of which is empty space, still we could never prove
that this space is empty out to an infinite distance. Far outside
of what we call the universe might still exist other universes
which we can never see.

It is a great encouragement to the astronomer that, although he
cannot yet set any exact boundary to this universe of ours, he is
gathering faint indications that it has a boundary, which his
successors not many generations hence may locate so that the
astronomer shall include creation itself within his mental grasp.
It can be shown mathematically that an infinitely extended system
of stars would fill the heavens with a blaze of light like that of
the noonday sun. As no such effect is produced, it may be
concluded that the universe has a boundary. But this does not
enable us to locate the boundary, nor to say how many stars may
lie outside the farthest stretches of telescopic vision. Yet by
patient research we are slowly throwing light on these points and
reaching inferences which, not many years ago, would have seemed
forever beyond our powers.

Every one now knows that the Milky Way, that girdle of light which
spans the evening sky, is formed of clouds of stars too minute to
be seen by the unaided vision. It seems to form the base on which
the universe is built and to bind all the stars into a system. It
comprises by far the larger number of stars that the telescope has
shown to exist. Those we see with the naked eye are almost equally
scattered over the sky. But the number which the telescope shows
us become more and more condensed in the Milky Way as telescope
power is increased. The number of new stars brought out with our
greatest power is vastly greater in the Milky Way than in the rest
of the sky, so that the former contains a great majority of the
stars. What is yet more curious, spectroscopic research has shown
that a particular kind of stars, those formed of heated gas, are
yet more condensed in the central circle of this band; if they
were visible to the naked eye, we should see them encircling the
heavens as a narrow girdle forming perhaps the base of our whole
system of stars. This arrangement of the gaseous or vaporous stars
is one of the most singular facts that modern research has brought
to light. It seems to show that these particular stars form a
system of their own; but how such a thing can be we are still
unable to see.

The question of the form and extent of the Milky Way thus becomes
the central one of stellar astronomy. Sir William Herschel began
by trying to sound its depths; at one time he thought he had
succeeded; but before he died he saw that they were unfathomable
with his most powerful telescopes. Even today he would be a bold
astronomer who would profess to say with certainty whether the
smallest stars we can photograph are at the boundary of the
system. Before we decide this point we must have some idea of the
form and distance of the cloudlike masses of stars which form our
great celestial girdle. A most curious fact is that our solar
system seems to be in the centre of this galactic universe,
because the Milky Way divides the heavens into two equal parts,
and seems equally broad at all points. Were we looking at such a
girdle as this from one side or the other, this appearance would
not be presented. But let us not be too bold. Perhaps we are the
victims of some fallacy, as Ptolemy was when he proved, by what
looked like sound reasoning, based on undeniable facts, that this
earth of ours stood at rest in the centre of the heavens!

A related problem, and one which may be of supreme importance to
the future of our race, is, What is the source of the heat
radiated by the sun and stars? We know that life on the earth is
dependent on the heat which the sun sends it. If we were deprived
of this heat we should in a few days be enveloped in a frost which
would destroy nearly all vegetation, and in a few months neither
man nor animal would be alive, unless crouching over fires soon to
expire for want of fuel. We also know that, at a time which is
geologically recent, the whole of New England was covered with a
sheet of ice, hundreds or even thousands of feet thick, above
which no mountain but Washington raised its head. It is quite
possible that a small diminution in the supply of heat sent us by
the sun would gradually reproduce the great glacier, and once more
make the Eastern States like the pole. But the fact is that
observations of temperature in various countries for the last two
or three hundred years do not show any change in climate which can
be attributed to a variation in the amount of heat received from
the sun.

The acceptance of this theory of the heat of those heavenly bodies
which shine by their own light--sun, stars, and nebulae--still
leaves open a problem that looks insoluble with our present
knowledge. What becomes of the great flood of heat and light which
the sun and stars radiate into empty space with a velocity of one
hundred and eighty thousand miles a second? Only a very small
fraction of it can be received by the planets or by other stars,
because these are mere points compared with their distance from
us. Taking the teaching of our science just as it stands, we
should say that all this heat continues to move on through
infinite space forever. In a few thousand years it reaches the
probable confines of our great universe. But we know of no reason
why it should stop here. During the hundreds of millions of years
since all our stars began to shine, has the first ray of light and
heat kept on through space at the rate of one hundred and eighty
thousand miles a second, and will it continue to go on for ages to
come? If so, think of its distance now, and think of its still
going on, to be forever wasted! Rather say that the problem, What
becomes of it? is as yet unsolved.

Thus far I have described the greatest of problems; those which we
may suppose to concern the inhabitants of millions of worlds
revolving round the stars as much as they concern us. Let us now
come down from the starry heights to this little colony where we
live, the solar system. Here we have the great advantage of being
better able to see what is going on, owing to the comparative
nearness of the planets. When we learn that these bodies are like
our earth in form, size, and motions, the first question we ask
is, Could we fly from planet to planet and light on the surface of
each, what sort of scenery would meet our eyes? Mountain, forest,
and field, a dreary waste, or a seething caldron larger than our
earth? If solid land there is, would we find on it the homes of
intelligent beings, the lairs of wild beasts, or no living thing
at all? Could we breathe the air, would we choke for breath or be
poisoned by the fumes of some noxious gas?

To most of these questions science cannot as yet give a positive
answer, except in the case of the moon. Our satellite is so near
us that we can see it has no atmosphere and no water, and
therefore cannot be the abode of life like ours. The contrast of
its eternal deadness with the active life around us is great
indeed. Here we have weather of so many kinds that we never tire
of talking about it. But on the moon there is no weather at all.
On our globe so many things are constantly happening that our
thousands of daily journals cannot begin to record them. But on
the dreary, rocky wastes of the moon nothing ever happens. So far
as we can determine, every stone that lies loose on its surface
has lain there through untold ages, unchanged and unmoved.

We cannot speak so confidently of the planets. The most powerful
telescopes yet made, the most powerful we can ever hope to make,
would scarcely shows us mountains, or lakes, rivers, or fields at
a distance of fifty millions of miles. Much less would they show
us any works of man. Pointed at the two nearest planets, Venus and
Mars, they whet our curiosity more than they gratify it.
Especially is this the case with Venus. Ever since the telescope
was invented observers have tried to find the time of rotation of
this planet on its axis. Some have reached one conclusion, some
another, while the wisest have only doubted. The great Herschel
claimed that the planet was so enveloped in vapor or clouds that
no permanent features could be seen on its surface. The best
equipped recent observers think they see faint, shadowy patches,
which remain the same from day to day, and which show that the
planet always presents the same face to the sun, as the moon does
to the earth. Others do not accept this conclusion as proved,
believing that these patches may be nothing more than variations
of light, shade, and color caused by the reflection of the sun's
light at various angles from different parts of the planet.

There is also some mystery about the atmosphere of this planet.
When Venus passes nearly between us and the sun, her dark
hemisphere is turned towards us, her bright one being always
towards the sun. But she is not exactly on a line with the sun
except on the very rare occasions of a transit across the sun's
disk. Hence, on ordinary occasions, when she seems very near on a
line with the sun, we see a very small part of the illuminated
hemisphere, which now presents the form of a very thin crescent
like the new moon. And this crescent is supposed to be a little
broader than it would be if only half the planet were illuminated,
and to encircle rather more than half the planet. Now, this is
just the effect that would be produced by an atmosphere refracting
the sun's light around the edge of the illuminated hemisphere.

The difficulty of observations of this kind is such that the
conclusion may be open to doubt. What is seen during transits of
Venus over the sun's disk leads to more certain, but yet very
puzzling, conclusions. The writer will describe what he saw at the
Cape of Good Hope during the transit of December 5, 1882. As the
dark planet impinged on the bright sun, it of course cut out a
round notch from the edge of the sun. At first, when this notch
was small, nothing could be seen of the outline of that part of
the planet which was outside the sun. But when half the planet was
on the sun, the outline of the part still off the sun was marked
by a slender arc of light. A curious fact was that this arc did
not at first span the whole outline of the planet, but only showed
at one or two points. In a few moments another part of the outline
appeared, and then another, until, at last, the arc of light
extended around the complete outline. All this seems to show that
while the planet has an atmosphere, it is not transparent like
ours, but is so filled with mist and clouds that the sun is seen
through it only as if shining in a fog.

Not many years ago the planet Mars, which is the next one outside
of us, was supposed to have a surface like that of our earth. Some
parts were of a dark greenish gray hue; these were supposed to be
seas and oceans. Other parts had a bright, warm tint; these were
supposed to be the continents. During the last twenty years much
has been learned as to how this planet looks, and the details of
its surface have been mapped by several observers, using the best
telescopes under the most favorable conditions of air and climate.
And yet it must be confessed that the result of this labor is not
altogether satisfactory. It seems certain that the so-called seas
are really land and not water. When it comes to comparing Mars
with the earth, we cannot be certain of more than a single point
of resemblance. This is that during the Martian winter a white
cap, as of snow, is formed over the pole, which partially melts
away during the summer. The conclusion that there are oceans whose
evaporation forms clouds which give rise to this snow seems
plausible. But the telescope shows no clouds, and nothing to make
it certain that there is an atmosphere to sustain them. There is
no certainty that the white deposit is what we call snow; perhaps
it is not formed of water at all. The most careful studies of the
surface of this planet, under the best conditions, are those made
at the Lowell Observatory at Flagstaff, Arizona. Especially
wonderful is the system of so-called canals, first seen by
Schiaparelli, but mapped in great detail at Flagstaff. But the
nature and meaning of these mysterious lines are still to be
discovered. The result is that the question of the real nature of
the surface of Mars and of what we should see around us could we
land upon it and travel over it are still among the unsolved
problems of astronomy.

If this is the case with the nearest planets that we can study,
how is it with more distant ones? Jupiter is the only one of these
of the condition of whose surface we can claim to have definite
knowledge. But even this knowledge is meagre. The substance of
what we know is that its surface is surrounded by layers of what
look like dense clouds, through which nothing can certainly be
seen.

I have already spoken of the heat of the sun and its probable
origin. But the question of its heat, though the most important,
is not the only one that the sun offers us. What is the sun? When
we say that it is a very hot globe, more than a million times as
large as the earth, and hotter than any furnace that man can make,
so that literally "the elements melt with fervent heat" even at
its surface, while inside they are all vaporized, we have told the
most that we know as to what the sun really is. Of course we know
a great deal about the spots, the rotation of the sun on its axis,
the materials of which it is composed, and how its surroundings
look during a total eclipse. But all this does not answer our
question. There are several mysteries which ingenious men have
tried to explain, but they cannot prove their explanations to be
correct. One is the cause and nature of the spots. Another is that
the shining surface of the sun, the "photosphere," as it is
technically called, seems so calm and quiet while forces are
acting within it of a magnitude quite beyond our conception.
Flames in which our earth and everything on it would be engulfed
like a boy's marble in a blacksmith's forge are continually
shooting up to a height of tens of thousands of miles. One would
suppose that internal forces capable of doing this would break the
surface up into billows of fire a thousand miles high; but we see
nothing of the kind. The surface of the sun seems almost as placid
as a lake.

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